NotInList Not working properly

I have a combo box on my form with the "NotInList" event firing this code:

    If MsgBox("Do you want to add this OWNER to the list?", vbYesNo) = vbYes Then
        DoCmd.OpenForm "frmOwnerAdd", , , , acFormAdd, acDialog, NewData
        Response = acDataErrAdded
    Else
        Response = acDataErrContinue
    End If

Select allOpen in new window

I've used this code many times in the past but for some reason after they close the pop-up form to enter the new owner into the table I get the "The text you entered isn't an item in the list" error. Then when you open the pull down on the combo you can clearly see that entry in the list. I have other databases that use this exact function and work fine. The combo box is bound to column 1 which is a "number" datatype. What also happens is after you click ok on the error message and then select the new entry from the pull down list and then tab out of that control the field goes blank but when you close and open the form the value is there. Something funky is going on and I can't figure it out. What am I missing?